regen/keywords.pl: remove obsolete comment

coresub_op() no longer hardcodes assumptions about the numeric values of
__FILE__, __LINE__, __PACKAGE__ keyword symbols.

Author: mauke

keywords.c

@@ -115,9 +115,6 @@ END
 read_only_bottom_close_and_rename($_, [$0]) foreach $c, $h;
 
 
-# coresub_op in op.c expects __FILE__, __LINE__ and __PACKAGE__ to be the
-# first three.
-
 __END__
 
  NULL